The pia arachnoid membrane as a constituent of the blood-brain barrier (BBB) has been cultivated and evaluated in regard to the monoamine uptake and pinocytotic activity which are restricted by the BBB in vivo. Both cell types (endothelium and pia) of the pia arachnoid membrane showed a limited uptake of catecholamines and serotonin. L-dopa was taken up by the endothelial but not by the pial cells while the reverse situation was observed in regard to the pinocytotic activity.